Filament and like bodies



Patented June 3, 1924.

NITED STATES PATENT OFFICE."

GOI QTON R. FONDA, OF SGHENECTADY, NEW YORKASSIGNOR 130' GENERAL COMPANY, A CORPQRATION OF NEW YORK.

nnnormo FI LAMENT AND LIKE BODIES.

No Drawing. Application filed July 17, 1919, Serial No. 311,564. Renewed April 28, 1924.

- tubes or X-ray tubes and the like, which during normal operation are maintained at high temperatures, gradually waste away and finally reach the end of their period of usefulness when the wasting away has become. excessive in amount or when the filament or other body breaks due to the Weakening thereof caused by such loss of material. In incandescent lamps, in both the vacuum type and the gas-filled type, the metal tungsten is almost universally used as a material for the filaments.

My invention comprises improvements in tungsten filaments, or in bodies of tungsten,

intended to operate at high temperatures,

whereby the disintegratimz; or evaporating tendency of the tungsten due to high temperature is materially reduced. F ilamentary bodies made according to my invention therefore may have, under the conditions of use, either a longer useful or burn-out life, if the im rovement in the material is to be availed of by operating the material at the same temperatures as heretofore, or a higher efliciency without curtailment of the length of life, or indeed, if desired, a compromise between these conditions.

I have found that the results which I'have indicated may be attained if a certain additional material is incorporated with the tungsten metal in a manner which I will set forth. I- am aware that it has been proposed to add to tungsten metal quantities of materials such as iron, nickel, uranium and the like, but such additions have, for various reasons, failed to increase the length of life or improve the efiiciency of the material as incandescent conductors. Thus, for example, it has been proposed to add 5% or more of iron to tungsten as an auxiliary metal to aid in manufacturing the filaments, the iron being then removed.

. I have found, however, as a result of long investigation, that in the case of iron a greatly improved filament material may be obtained by producing a combination or perhaps a 5011(1 solution of iron and tungsten of such a nature thatthe iron constitutes 1 only an extremely small proportion of the whole, Where the filaments of this material are made by the squirting process I have found that the most desirable results are obtalned with mixtures containing originally about 5- or 1% of iron by weight. filaments produced from this mixture are operated in a treating bottle or otherwise for a considerable time at about 2100 degrees G, a temperature which I have found to give good results. This gives an opportunity for the two metals to combine so as to form a more or less permanent alloy or The solid solution. During this treating operation, and before the combination of'the iron with the tungsten is complete, considerable of'the iron originally introduced is evaporated as such from the filament.

Thus,

after the heat treatment, which in some cases has lasted as long as fifteen hours, the iron content is found to have fallen to something like 0.2% of iron by weight or less. The heat treatment is thus such as to cause a reduction of the iron content to about twenty per cent of the original iron content.

In making filaments by the squirting process I may employ any one of the well known methods, such as the amalgam process in which the mixed metallic powders are made into an amalgam with an alloy of mercury. bismuth and cadmium, or I may use the celloidin squirting process, in which the binder is a solution of celloidin in amyl acetate and castor oil, celloidin being a well known German preparation of nitrocellulose. In the amalgam process the firing and treating of the squirted filament is done in a vacuum in the usual way, while in the celloidin process it is done in hydrogen. The carrying out of these squirting processes is well understood in the art and therefore requires no special description. Instead of employing the squirting process for forming the filamentary bodies, I

'therethrough in an atmosphere of hydrogen. The heat treatment required for the proper amalgamationof the iron and tungsten is obtained in this case during the treatment of the rod or slug in a hydrogen atmosphere in the treating bottle. As this treatment necessarily takes place at an exceedingly high temperature in order to consolidate the material of the rod or slug, more iron must be rovided originally in order to allow for the greater loss of iron by evaporation. Thus, instead of starting with say i of one per cent of iron, as is done in the case where the squirting process is employed, I have in one instance added to the mixture from which the slug or rod is made something like 2% of iron by weight. After the rod orslug had been subjected to the heat treatment in hydrogen in the treating bottle the amount of iron which then re,- mained in the rod or slug was found to be reduced to something like 0.1% by weight. The rods or slugs thus produced were then drawn into wire by a drawing process like that used for drawing tungsten wire.

When filamentary bodies are made as above described, and containing the small amounts of iron as set forth, the iron probably being present in the bodies in a peculiarly stable state of combination, I have found that such bodies are capable of giving results which surpass those obtainable from ordinary tungsten filaments as now known to the art. Thus, for example, my improved filaments when operated at the efficiences common in present day incandescent lamps have exhibited a length of life, up to the point where the candle power, has been reduced to 80% of'their original candle power, which is something like 30% longer than that of ordinary tungsten lamps, while the life up to burn out is something like double that of ordinary tungsten filaments. When my improved filaments are operated as filaments of gas filled lamps instead of in a vacuum the burn-out life is something over 60% longer than that of ordinary tungsten filaments. By gas filled lamps I refer to lamps such as are set forth in U. S. Patent to Langmuir, No. 1,180,159,

A ril 18, 1916. a

lf more than about 1% of iron be present I have found that the 80% life is shortened and, as the percentage of iron is further increased, the burn-out life becomes continuously shorter until it becomes lessthan that of ordinary tungsten filaments, while with still more iron the melting point may be reduced below that corresponding to the normal operating temperature of the filament. Where materially less than 0.1%

the improvements characteristic of my invention are obtained only with very small quantities of iron present, the iron being under these conditions in stable combination with the tungsten whereby the vapor pressure or Wasting tendency of the lament at high temperature is greatly reduced as compared with that of the ordinary tungsten filament. The melting point of the resulting filament which contains iron is slightly reduced as compared with tungsten but as the operating temperature of the filament, even in a gas filled lamp, is well below that' of the melting point of the alloy, this reduction is of no consequence.

Where the filament is produced by the use of the drawing process, I have found that the use of iron has an important effect in preventing or reducing offsetting. An examination of the crystalline structure in cross sections of such filaments with and without iron presenttherein illustrates the effectiveness of the iron content in preventing ofi'setting. Crystal sizes in filaments of lam s after life test are found to be largest int e case of filaments in which no iron was present and to be the smallest in those filaments containin a certain amount of iron say in the neigh orhood of 0.1%. With increasing amounts of iron the crystal or grain sizeis progressively increased until at about 1% it becomes about as large or coarse as that in tungsten in which no iron is present. This same variation of crystal size with iron content within the limits indicated is shown initially in the filaments immediately after preparation, and for any one percentage of iron the crystal size varies butslightly during the life of the filament, and it has been found to increase but slightly, for instance, in filaments tested for 4000 hours in argon gas at 2600 C. This persistence of small crystals prevents the formation of large intercrystalline cleavage planes across the filament and thereby reduces the corresponding tendency of the filament to offset during operation. Moreover, as small crystal size or fine grain is ":--usually associated with increased tensile strength and;.;decreased brittleness, the filaments made in accordance with my inven tion, and containing less than 0.2% of iron, show abnormal strength and ruggedness.

The smallcrystal size which 'I have mentionedis characteristic both of the squirted filaments as well as the drawn filaments, and it is possible that this fact is in some way connected with the reduced vapor pressure of the material when used as filaments What I claim as new and desire to secure by Letters Patent of the United States, is,--

1. A tungsten body or conductor containing iron, said body being markedly stable as against the effects of high temperature, the

iron being in an appreciable amount but not more than one per cent by weight of the total and being so combined with the tungsten that the crystalline structure is finer grained after long subjection of the conductor to high temperatures than'the structure of a pure tungsten conductor subjected to the same condltion.

2. A filament capable of operating at high temperatures and of resisting ofisetting effectlvely, comprising a body of tungsten having a quantity of iron materially less than one per cent present therein, the resulting body being characterized by a crystalline structure which is finer grained and is more'stable than the crystalline structure of pure tungsten which has been subjected to the same condition.

3. A filament for incandescent electric lamps and for otherpurposes comprising I tungsten and a quantity of iron in amount of a out one-tenth to two-tenths of the total, the iron being so combined with the tungsten as to present a structure of small grains in such stable, condition that long subjec tion to high tem erature does not increase the grain size su ciently to cause objectionable ofisetting.

4. A filament for incandescentelectric lamps and for other purposes comprising tungsten and (iron, the iron being present in temperatures than a filament of pure tungsten.

5. A filament for incandescent lamps and for other purposes comprising tungsten and iron, the iron being present in amount less than one per cent of the whole and so combined with the tungsten as to produce a finegrained crystalline structure of such stability against grain growth that the filament during operation at incandescence. effectively reslsts offsetting and vaporizes or wastes away at a slower rate than a filament of pure tungsten.-

6. Afilament which resists ofi'settin and which va orizes or wastes away more s owly than a fiiiiment of pure tungsten, the same comprising a body of tungsten combined with iron,'the amount of iron associated ale with the tungsten having been such that the crystalline structure of the filament is relatively fine-grained and stable as against long continued high tem erature, the iron present in the resulting lament being materially less than one per. cent of the whole.

7. A body of combined tungsten and iron,

tendency to waste away at a given high temperature than such apure tungsten b0 8. The process of making filaments for incandescent lamps which consists inshaping into elongated conductors a mixture of tungsten and iron, the iron being present in amounts not in excess of one to two per cent of the whole, and heating said conductors to a temperature of about 2100 C. for h of time suificientto combine the iron in part with the tungsten to form a fine-grained material which'is more resistant to the action of high temperature than pure tungsten, the iron content being reduced by evaporation during said treatment to a residual amount of materially less than one per cent.

9. A tun ten filament containing iron In amounts 0 about one to two-tenths of one per cent and being derived from a filament containing from one-half to two per centof iron b subjection to about 2100 C. said filament aving a finer grain structure than.

pure tungsten which has been subjected to the same conditions and which is more stable than pure tungsten at the operating temperatures of incandescent lamps. I

10. The process of making filaments for incandescent lamps which consists in forming wire consisting largely of tungsten and containing less than two per cent of iron, heating said wire to a temperature of about 2100 C. for a sufiicient length of time to produce a'material having a finer grained structure than pure tungsten develops when subjected to the same conditions and sulficient to reduce the iron content to about one-tenth of one per cent.. i i

In witnesswhereof, I have'hereunto set my hand this 16th day pf July, 1919.

' 'GORTON R. ,FONDA.. 

